The Hypogeum in Paola, Malta, is a subterranean structure dating to the Saflieni phase in Maltese prehistory. Thought to be originally a sanctuary, it became a necropolis in prehistoric times. It is the only prehistoric underground temple in the world. It was closed to visitors between 1992 and 1996 for restoration works; since it reopened only 80 people per day are allowed entry and there can be many weeks wait to get a ticket. Malta's Hypogeum was discovered by accident in 1902 when workers cutting cisterns for a new housing development broke through its roof. The workers tried to hide the temple at first, but eventually it was found. The Hypogeum is a World Heritage Site